The Lead concentrations in water

I'm in dire need of help with a reaserch project asap

My hypothesis is:

The lead concentrations in water travelling through lead pipes is greater when the taps are first opened than after they have ran for some time

My problem is
1. when can i expect the concentrations to lower so i can be more specific in my hypothese i would like to write somthing along the lines of
The lead concentrations in water travelling through lead pipes is greater when the taps are first opened than after they have ran for five minutes
And give a good scientific reason for the time specified
2. I need a scientific method to test this hypotheses
and a structured guide line for the write up
3. I also need to relate the whole investigation to health issues
4. as you can tell i need lots of facts and figures to relate my findings to